The present invention relates to ink-jet printing paper suited for obtaining a high quality image free from the mixed color running of ink and the like, in performing multi-color ink-jet printing by use of water color ink, and an ink-jet printing method using the same printing paper.
Conventionally, as ink-jet printing paper, there has been proposed ink-jet printing paper whose ink absorbing property is improved, in order to obtain an image of a higher quality.
For example, Japanese Patent Examined Publication No. Sho. 60-27588 discloses a printing paper which is formed by applying a paint having a higher ink absorbing property (of the order of 11 to 13 g/m.sup.2 in a dry amount of paint) on original paper of a higher sizing degree.
However, since a relatively large amount of paint is applied to the printing paper, such printing paper gives different feel and appearance from so called ordinary paper such as copying paper used in an office and the like, and such printing paper is expensive. Further, since the paint layer thus applied is poor in strength, when it is folded or rubbed, powder drop is easily generated in the paper. The paper powder can be attached to a feeding roll for the paper, which can result in the poor paper feeding and also in the clogged ink-jet head.
In order to solve the above-mentioned problems, as disclosed in Japanese Patent Laid-Open No. Hei. 2-16079, there is proposed printing paper in which a paint layer (or, an ink receiving layer) is formed thin and the roughness factor of the surface of the paint layer is set not less than 10 ml/m.sup.2 or the Beck smoothness of the paint layer is set not more than 20 sec. Also, as disclosed in Japanese Patent Laid-Open No. Hei. 2-16078, there is proposed an ink-jet printing method using printing paper in which a paint layer is formed thin (the dry amount of paint is of the order of 0.6 to 10 g/m.sup.2) and the amount of initial transfer of the printing paper (that is, the ink absorbing capacity in the time of contact, 10 ms, of the printing paper with ink according to a blister method) is more than the maximum printing density (that is, an upper limit amount of ink to be applied by a printer).
Concerning the printing paper disclosed in the above-mentioned Reference No. Hei. 2-16079, the paper is caused to minimize the amount of paint to be applied (that is, the amount of paint when dried is approximately 0.6 to 6.0 g/m.sup.2) and to rough the surface of the paint layer, to thereby prevent powder drop from generating in the printing paper and prevent an ink running at a boundary portion of different colors (that is, bleeding) in the printing. But, specifically, when performing a higher density printing of a definition of 300 dpi or more at a higher speed, there arises a problem in the printing paper that mixed color bleeding occurs in the printing portion where different colors of ink are superimposed on one another. The reason why such mixed color bleeding occurs is that, in the higher-speed and higher density printing, a time period from the printing of a first color to the printing of a second color is too short and the applied amount of the ink per unit area becomes large and, therefore, these two colors cannot be absorbed quickly by only roughening the paint layer surface thereof. Also, in the printing paper, since the paint layer surface is roughened, the ink flows into the recessed portion of the roughened surface, and the ink is disturbed to spread over the paper surface, which results in the ununiform dot shapes. As a result, the quality of the image is lowered.
Further, in the printing method disclosed in the above-mentioned reference No. Hei. 2-16078 as well, when executing a high density printing with the definition of 300 dpi or more at a higher speed, there is the mixed color bleeding in the printing portion where different colors of ink are superimposed.
At the time, the contact time period 10 ms, between the printing paper and ink according to the blister method regulating the initial transfer amount of the printing paper used in the printing method, corresponds to the wetting period of ink on the surface of the printing paper and such wetting period is greatly influenced by the roughened state of the surface of the printing paper. For the reason, in order to make the initial transfer amount of the printing paper in the contact time period 10 ms larger than the ink discharge amount in the time of the upper limit of the printing density, roughness of the printing paper surface must be increased, with the result that, in the printing paper as well, the ink flows into the recessed portion of such roughened surface, which makes it impossible to prevent the mixed color bleeding sufficiently and also makes ununiform the shapes of dots, so that the quality of the image is lowered.